Browsing by Subject "Bedrock"

Now showing 1 - 11 of 11
  • Thumbnail Image
    Item
    C-29 Geologic Atlas of Clay County, Minnesota [Part A]
    (Minnesota Geological Survey, 2014) Bauer, Emily J.
    Surface and subsurface geology of Clay County, Mn., also includes data-base information, subsurface stratigraphy, bedrock topography, depth-to-bedrock and sand distribution models.
  • Thumbnail Image
    Item
    Field, experimental and numerical investigations into the mechanisms and drivers of lateral erosion in bedrock channels
    (2014-01) Fuller, Theodore Kent
    The process of lateral erosion in bedrock channels is poorly understood. This thesis sheds light on the mechanisms of lateral bedrock erosion as well as the larger scale drivers of lateral erosion. Contained in this thesis are three distinct studies: a field-based study that investigates the drivers of lateral planation of strath surfaces; an experimental study that seeks to identify specific mechanisms of lateral erosion; and a numerical modeling study that seeks to corroborate the findings of the experimental study and permit exploration of parameter space. The field study (Chapter 1) concludes that lateral planation of strath surfaces in the dominant channel erosion process during periods of elevated sediment supply. This study further concludes that the elevated sediment supply conditions were driven by changes in climate. The experimental study (Chapter 2) concludes that the deflection of saltating bedload particles by fixed roughness elements into the wall is an effective mechanism of erosion. In addition, the experimental study identifies a minimum roughness threshold that must be crossed before significant lateral erosion can occur. Finally, the experimental study suggests that once the roughness threshold is crossed (i.e. moving from a smooth bed devoid of roughness elements to a bed with roughness elements), further increases in bed roughness do not produce ever increasing rates of lateral erosion. Rather, an erosion rate plateau is reached shortly after the roughness threshold is crossed. The numerical modeling study (Chapter 3) corroborates the findings of the experimental study and demonstrates, from first principles, that lateral erosion by deflected bed load particles is an effective mechanism of lateral bedrock erosion. In addition, this study identifies an important trade-off between increased deflection surface area from larger roughness elements and the increased form drag associated with the larger roughness elements. Here, the increase in the number of particle deflections is offset by the decrease in particle kinetic energy on impact, resulting in the erosion rate plateau observed in the physical experiments.
  • Thumbnail Image
    Item
    Geologic Map Series 1. Bedrock Geology of Duluth and Vicinity St. Louis County, Minnesota
    (Minnesota Geological Survey, 1963) Taylor, Richard B.
    Duluth, Minnesota, is on the northwest limb of the Lake Superior syncline, a northeast-trending structure of Precambrian age. The north- west limb of the syncline dips 10-20 degrees S.E. toward Lake Superior and is dominated by the Duluth Gabbro Complex, a huge sill-like mass with crescentic outcrop that extends almost 150 miles from Duluth to near Hovland. At Duluth the gabbro complex lies on the Thomson Formation, and apparently was intruded along the surface of unconformity below the Keweenawan rocks. The gabbro complex was formed by multiple intrusion, and consists of an older anorthositic gabbro and a younger layered gabbro and related intrusions. Keweenawan flows above the gabbro mass are cut by diabase sills. The basalt flows at one locality currently are being quarried as a source of crushed rock for concrete aggregate.
  • Thumbnail Image
    Item
    M-194 Bedrock Geology of the Twin Cities Ten-County Metropolitan Area, Minnesota
    (2013-08-01) Mossler, John H.
    This regional map is partly a compilation of existing maps of bedrock geology in the metropolitan area and partly a remapping of bedrock in areas where the existing maps were out of date because of the acquisition of new subsurface data.
  • Thumbnail Image
    Item
    M-197 Bedrock Geology of the International Falls and LittleFork 30' x 60' Quadrangles, northern Minnesota
    (Minnesota Geological Survey, 2014-09-25) Jirsa, Mark A.; Boerboom, Terrence J.; Chandler, V.W.
    The map depicts a complex history of volcanism, sedimentation, intrusion, multiple events of migmatization involving partial melting and melt dispersion, and several periods of deformation and metamorphism. It lies within the southern exposed extent of the Archean Superior Province. In northern Minnesota, the province is divided into three major tectonomagmatic terranes known as the Wabigoon, Quetico, and Wawa subprovinces. The publication shows the locations of mapped bedrock outcrops, structural measurements, interpreted bedrock geology in both map and cross-section views, and associated explanations. Ancillary imagery includes maps of regional geologic setting, index of archived mapping incorporated into this interpretation, and schematic depiction of geologic history.
  • Thumbnail Image
    Item
    OFR10-04, Preliminary Bedrock Geologic Map of Part of the 2007 Ham Lake Fire Area: Portions of Conners Island, Gillis Lake, Long Island Lake, and Munker Island 7.5-minute quads, northeastern Minnesota, and Ontario, Canada
    (Minnesota Geological Survey, 2010) Jirsa, M.A.
    This map describes bedrock geology along the Gunflint Trail in a part of the area burned during the Ham Lake forest fire in 2007. The map covers only a portion of the fire area because much of the burn lies in Canada, or within plutonic rocks that generally lack significant mappable variations. Only the southeastern corner of the map area was not burned—the burn extends to the north and east beyond the map sheet. The western edge of the map is coincident with the area of the 2006 Cavity Lake fire, which was mapped previously by Jirsa and Starns (2008).
  • Thumbnail Image
    Item
    OFR10-05, Preliminary Bedrock Geologic Map of the Grand Marais 7.5' quadrangle, Cook County, Minnesota
    (Minnesota Geological Survey, 2010) Boerboom, T.J.; Green, J.C.
    Bedrock geologic map of Grand Marais 7.5' quadrangle
  • Thumbnail Image
    Item
    OFR13-01, Preliminary Bedrock Geologic Map of the Pagami Creek Fire Area, Lake and Cook Counties, Northeastern Minnesota
    (2013) Jirsa, M.A.; Leu, A.; Miller, J.D., Jr.
    This geologic map encloses the area burned by the 2011 Pagami Creek forest fire—one of the largest in Minnesota history. It covers all or parts of fifteen 7.5-minute quadrangles, and lies within parts of the Superior National Forest and Boundary Waters Canoe Area Wilderness. The map area contains bedrock units spanning a wide range of ages from Archean to Mesoproterozoic, and a generally thin and discontinuous cover of glacial sediment. The majority of the map portrays intrusive units of the Mesoproterozoic Duluth Complex, including portions of the anorthositic and layered series’. Although the map primarily depicts bedrock geology, some features of glacial origin are also portrayed. The map is considered preliminary largely because geologic mapping in the area by a number of authors is ongoing—a final version is likely to be published in coming years.
  • Thumbnail Image
    Item
    Regional and Local Geologic, Mineralogic, and Geochemical Controls of Industrial Clay Grades in the Minnesota River Valley and the Meridian Aggregates Quarry, St. Cloud, Minnesota
    (University of Minnesota Duluth, 1991-07) Hauck, Steven A; Heine, John J; Shurr, George W; Toth, Thomas A; Tozer, Mary K; Victory, Denise A
    The purpose of this project is to determine the regional and local geological, mineralogical, and geochemical factors that control the distribution and grade of the industrial clays in the Minnesota River Valley (MRV) between Redwood Falls and Fairfax, Minnesota and at the Meridian Aggregates Quarry (MAQ), St. Cloud, Minnesota. These controlling factors fall into three broad categories: 1) bedrock controls - parent rock characteristics; 2) physical controls - faults, paleotopography, etc.; and 3) chemical controls.
  • Thumbnail Image
    Item
    RI-70, Characterization of the Franklin Peridotite and Other Similar Intrusions in East-Central and Southwestern Minnesota
    (2014) Boerboom, Terrence J.
    Outcrops of peridotite adjacent to the Minnesota River near the town of Franklin in Renville County were sampled and petrographically characterized as part of a small study funded by the Minnesota Department of Natural Resources in 1997. That study obtained mineral separates with the intent of examining them for kimberlite indicator minerals. The results were not formally published, but rather summarized in an unpublished final report to the Minnesota Department of Natural Resources titled "Mineral Investigations of Franklin Kimberlites." In addition to petrographic and geochemical characterizations, ground magnetic traverses were made across the outcrop area in order to quantify the size and shape of the peridotite body. Based on simple ground magnetic surveys, the peridotite body is approximately 1 square kilometer (0.4 square mile) in area. The peridotite in the outcrops is extensively silicified, most likely by low-temperature alteration associated with lateritic weathering beneath Cretaceous sedimentary strata. Peridotite that is not silicified is composed of olivine (serpentinized), orthopyroxene, hornblende, magnetite, and minor spinel, phlogopite, ilmenite, and sulfide minerals; all the silicate phases are Mg-rich. The silicified peridotite contains abundant secondary quartz and chalcedony, but the silicification did not affect the Fe/Mg ratio, as both silicified and unsilicified peridotite have Mg numbers of 87 to 88. The Franklin peridotite is similar to ultramafic peridotite and pyroxenite bodies in east-central Minnesota, as well as the Cottonwood peridotite body intersected by drilling in northern Lyon County, 55 kilometers (34 miles) west–northwest of the Franklin peridotite and south of the Minnesota River valley. The peridotites in east-central Minnesota are between 1,770 and 1,791 Ma in age, whereas the age of the Franklin and Cottonwood peridotites is unknown.
  • Thumbnail Image
    Item
    S-22, Geologic Map of Minnesota, Precambrian Bedrock Geology
    (2012) Jirsa, M.A.; Boerboom, T.J.; Chandler, V.W.
    This map of the Archean and Proterozoic (Precambrian) geology of Minnesota is identical with MGS State Map S-21, except it portrays an interpretation beneath Phanerozoic (Paleozoic and Mesozoic) strata inferred from geophysical maps and drill core.